Wireless communication networks contact individual subscribers' user equipment (UE) that is camped on a base station or Node-B, by transmitting a “page” unique to the UE throughout the cell or sector. The page may take different forms in systems operating under different protocols (W-CDMA, GSM, UMTS, etc.). The paged UE is directed to a particular channel, such as a control channel, to receive more detailed information, such as the network event prompting the page (incoming call, location update, etc.) and how it should respond. One form of paging UEs comprises assigning to each UE camped on a base station, a section of a frame of a paging indicator channel, to monitor for a paging indicator (PI). If the UE detects a PI, it monitors a predetermined channel after a predetermined delay to obtain control information regarding the page.
A straightforward way of monitoring for the PI is to accumulate a predetermined number of received bits at the UE's assigned frame position to generate a decision variable, and compare the decision variable against a threshold. For example, where bits are modulated as +1/−1, the threshold may be 0. That is, a decision variable greater than 0 indicates the presence of a PI, and a decision variable less than 0 indicates no PI was transmitted. This simple approach mathematically achieves the minimum error probability. However, the mathematical minimum error probability is only optimal if the two error cases—missing a transmitted PI and falsely detecting a PI where none was transmitted—have equal consequence. In real-world systems, the former error has far greater consequences than the latter.
If a UE misses a transmitted PI, it will fail to subsequently monitor a control channel, and will not response to the network. The UE may thus miss an incoming call, it may cause the network to assume the UE has left the cell or powered down, or have some other deleterious impact on network mobility management. Recovery from this error may require significant processing by higher order protocol layers. On the other hand, if the UE falsely detects a PI where none was transmitted, the UE simply monitors its assigned control channel for system signaling, which it will not receive. The cost is simply the power expended to needlessly monitor the control channel for one duration.
Under a scheme of simple thresholding against a fixed, standard value, as described above, the probability of correct PI detection depends on radio conditions, and cannot be guaranteed to any required degree of accuracy. For example, under radio conditions yielding a high signal to interference ratio (SIR), there is a low probability of missed PI detection. However, under a low SIR, the probability of missed PI detection increases.